Common rail injector

ABSTRACT

The invention relates to a common rail fuel injector having an injector housing with a fuel inlet in communication with a central high-pressure fuel reservoir outside the injector housing and with a pressure chamber inside the injector housing. A control valve that assures that a nozzle needle lifts from a seat when the pressure in the pressure chamber is greater than the pressure in a control chamber that communicates with the fuel inlet via an inlet throttle and with a relief chamber via a fuel outlet. The control chamber is integrated with the end, remote from the combustion chamber, of the nozzle needle.

This application is a 35 USC 371 application of PCT/DE 00/02532 filed onAug. 1, 2000 and a continuation-in-part application of application Ser.No. 09/319,533, filed Jul. 21,1999 now U.S. Pat. No. 6,247,452.

FIELD OF THE INVENTION

The invention relates to a common rail injector for injecting fuel in acommon rail injection system of an internal combustion engine, whichsystem has an injector housing with a fuel inlet that is incommunication with a central high-pressure fuel reservoir outside theinjector housing and with a pressure chamber inside the injectorhousing, from which fuel subjected to high pressure is injected as afunction of the position of a control valve that assures that a nozzleneedle movable back and forth and received in a longitudinal bore of theinjector axially counter to the prestressing force of a nozzle springthat is received in a nozzle spring chamber, lifts from a seat when thepressure in the pressure chamber is greater than the pressure in acontrol chamber that communicates with the fuel inlet via an inletthrottle and with a relief chamber via a fuel outlet.

DESCRIPTION OF THE PRIOR ART

In common rail injection systems, a high-pressure pump pumps the fuelinto the central high-pressure fuel reservoir, which is called a commonrail. From the high-pressure fuel reservoir, high-pressure lines lead tothe individual injectors, which are assigned to the engine cylinders.The injectors are triggered individually by the engine electronics. Therail pressure prevails in the pressure chamber and at the control valve.When the control valve opens, fuel subjected to high pressure reachesthe combustion chamber, past the nozzle needle that is lifted counter tothe prestressing force of the nozzle spring.

In conventional injectors, of the kind known for instance from GermanPatent Disclosure DE 197 24 637 A1, relatively long nozzle needles areused. In operation, because of the high pressures and the rapid loadchanges, very strong forces act on the nozzle needle. These forces causethe nozzle needle to be stretched and compressed in the longitudinaldirection. This in turn means that the nozzle needle stroke varies as afunction of the forces acting on the nozzle needle.

The object of the invention is to furnish a common rail injection systemwith a small structural volume that is simple in design and can beproduced economically. In particular, even at a high nozzle needlespeed, good closing performance should be assured.

In a common rail injector for injecting fuel in a common rail injectionsystem of an internal combustion engine, which system has an injectorhousing with a fuel inlet that is in communication with a centralhigh-pressure fuel reservoir outside the injector housing and with apressure chamber inside the injector housing, from which fuel subjectedto high pressure is injected as a function of the position of a controlvalve that assures that a nozzle needle movable back and forth andreceived in a longitudinal bore of the injector axially counter to theprestressing force of a nozzle spring that is received in a nozzlespring chamber, lifts from a seat when the pressure in the pressurechamber is greater than the pressure in a control chamber thatcommunicates with the fuel inlet via an inlet throttle and with a reliefchamber via a fuel outlet, this object is attained in that the controlchamber is integrated with the end of the nozzle needle remote from thecombustion chamber. This furnishes a compact common rail injector whichassures rapid closure of the nozzle needle. The control chamber can bemade smaller than in conventional injectors, which makes for a rapidresponse performance by the injector. Embodying the injector accordingto the invention makes rail pressures of up to 1800 bar possible.

One particular type of embodiment of the invention is characterized inthat in the end, remote from the combustion chamber, of the nozzleneedle a substantially cylindrical recess is provided, in which an outercircumferential portion of a bush is axially displaceably received witha sealing effect, the end face, remote from the combustion chamber, ofwhich bush is pressed by the prestressing force of the nozzle springagainst the injector housing, and the interior of which bushcommunicates with the fuel outlet. The bush offers the advantage thatthe control chamber and the nozzle spring chamber can be combined on theend, remote from the combustion chamber, of the nozzle needle withoutthe volume of the control chamber being dependent on the installationspace for the nozzle spring. It is therefore possible to build in anozzle spring with a high spring stiffness, which assures good closureof the nozzle needle. As a result, the duration and instant of injectioncan be defined exactly.

A further particular type of embodiment of the invention ischaracterized in that on the end of the bush remote from the combustionchamber, a collar is embodied, which forms an abutment for the nozzlespring that is prestressed counter to the end, remote from thecombustion chamber, of the nozzle needle. In the context of the presentinvention, the nozzle spring has a dual function. First, the closingmotion of the nozzle needle is effected by the prestressing force of thenozzle spring, and second, the control chamber volume is defined by theprestressing force of the nozzle spring in conjunction with the pressurein the control chamber.

Another particular type of embodiment of the invention is characterizedin that on the face end of the bush remote from the combustion chamber,which is in contact with the injector housing, a biting edge isembodied. As a result, the control chamber is separated from the nozzlespring chamber surrounding the bush.

Another particular type of embodiment of the invention is characterizedin that the fuel inlet communicates with the pressure chamber via thenozzle spring chamber, and that the nozzle needle is guided between thenozzle spring chamber and the pressure chamber. This offers theadvantage that the nozzle needle guide no longer has any sealingfunction. This makes the demands in terms of quality of the guide lessstringent, leading to economies in production. Since the same pressureprevails on both sides of the guide, guide leakage no longer occurs.

A further particular type of embodiment of the invention ischaracterized in that at least one flat face, past which fuel from thenozzle spring chamber can reach the pressure chamber, is embodied on thenozzle needle between the nozzle spring chamber and the pressurechamber. This type of embodiment offers advantages especially withregard to the high-pressure strength.

Another particular type of embodiment of the invention is characterizedin that the inlet throttle is integrated with the nozzle needle or thebush. The inlet throttle serves to prevent pressure surges in operation.

A further particular type of embodiment of the invention ischaracterized in that the nozzle needle stroke is defined by the spacingbetween the nozzle needle and the bush. This purely mechanical nozzleneedle stroke end stop offers the advantage that the nozzle needlestroke is exactly replicable. As a result, the course of injection canbe shaped reliably. So-called hydraulic sticking is avoided.

A further particular type of embodiment of the invention ischaracterized in that on the end of the bush remote from the combustionchamber, an auxiliary control chamber is embodied, which communicatesvia an inlet throttle with the nozzle spring chamber and via anauxiliary throttle with the cylindrical recess in the nozzle needle. Inthis type of embodiment, during the closing motion of the nozzle needle,the bush can be lifted from its seat on the injector housing. As aresult, the auxiliary control chamber and the cylindrical recess thatforms the actual control chamber can be more quickly filled with fuelthat is at high pressure. This further speeds up the closing motion ofthe nozzle needle.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, characteristics and details of the invention willbecome apparent from the ensuing description, in which various exemplaryembodiments of the invention are described in detail in conjunction withthe drawings, in which;

FIG. 1 is a first exemplary embodiment of an injector of the invention,in a longitudinal section through the injector housing; and

FIG. 2 is a second exemplary embodiment of an injector of the invention,in a longitudinal section through the injector housing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first exemplary embodiment, shown in longitudinal section in FIG. 1,of the injector of the invention has an injector housing identifiedoverall by reference numeral 1. The injector housing 1 includes a nozzlebody 2, which with its free end protrudes into the combustion chamber ofthe internal combustion engine to be supplied. With its end face remotefrom the combustion chamber, the nozzle body 2 is braced axially againsta retaining body 3 by means of a lock nut (not shown).

An axial guide bore 4 is recessed out of the nozzle body 2. A nozzleneedle 5 with a tip 6 is guided axially displaceably in the guide 4. Asealing face is embodied on the tip 6 of the nozzle needle 5 andcooperates with a sealing seat that is embodied on the nozzle body 2.The diameter of the sealing seat is indicated by d_(s). If the tip 6 ofthe nozzle needle 5 is located with its sealing face in contact with thesealing seat, an injection port 7 in the nozzle body 2 is closed. Whenthe nozzle needle tip 6 lifts from its seat, fuel subjected to highpressure is injected through the injection port 7 into the combustionchamber of the engine. The stroke of the nozzle needle 5 is indicated bythe letter H.

The nozzle needle 5 has three regions of different diameters d₁, d₂ andd₃, beginning at the tip 6. The diameter d₁ is somewhat smaller than thediameter d₂. Because of the difference in diameter between d₂ and d₁, anannular chamber 8 is created in the vicinity of the end of the nozzlebody 2, toward the combustion chamber or tip 6. The annular chamber 8 isalso called a pressure chamber. The diameter d₂ of the nozzle needle 5,in the present example, is equivalent to the diameter d₃ at the nozzleneedle 5. The diameter d₂ is also called the guide diameter. Thediameter d₃ is also called the control diameter. In the presentexemplary embodiment, the outside diameter d₂ of the nozzle needle 5 isequal to the inside diameter d₃ of the recess 14 in the end of thenozzle needle 5 remote from the combustion chamber or tip 6. However,the diameter d₃ may also be smaller than the diameter d₂.

In the guide portion of the nozzle needle 5 having the diameter d₂,there is at least one flat face 9. The flat face 9 creates acommunication between a nozzle spring chamber 10 and the pressurechamber 8. The nozzle spring chamber 10 is surrounded by the nozzle body2 and the retaining body 3. A fuel inlet 11 is disposed in the retainingbody 3 and discharges into the nozzle spring chamber 10. A nozzle spring12 is disposed in the nozzle spring chamber 10. The nozzle spring 12 isbraced on the end face of the nozzle needle 5 remote from the combustionchamber or tip 6. A cylindrical recess 14, which surrounds a controlchamber 15, is located in the center of the end face of the nozzleneedle 5 remote from the combustion chamber or tip 6. A bush 16 isguided on its outer jacket face in the region of the cylindrical recess14 having the diameter d₃. On the end of the bush 16 remote from thecombustion chamber or tip 6, there is a collar 17, which forms anabutment for the prestressed nozzle spring 12. A biting edge 18, whichis in contact with the retaining body 3, is also embodied on the endface of the bush 16 remote from the combustion chamber of the engine orthe tip 6 of the nozzle needle.

The control chamber 15 communicates with the nozzle spring chamber 10via an inlet throttle 19. The control chamber 15 also communicates viathe interior of the bush 16 with a fuel outlet 20. An outflow throttle21 is located in the fuel inlet 20. The fuel inlet 20 is closed by acontrol valve member 22. If the control valve member 22 lifts from itsseat, the fuel outlet 20 is connected to a pressure relief chamber (notshown).

The common rail injector shown in FIG. 1 functions as follows: Via thefuel inlet 11, fuel subjected to high pressure flows out of the railinto the nozzle spring chamber 10. From there, the fuel at high pressureon the one hand reaches the control chamber 15 via the inlet throttle 19and on the other flows past the flat face 9 to reach the pressurechamber 8. The diameter ratios are selected in a known manner such thatthe nozzle needle 5, as a result of the high pressure in the controlchamber 15, is located with its tip 6 in contact with the nozzle needleseat. When the control valve member 22 opens, the control chamber 15 isrelieved, and the nozzle needle tip 6 lifts from its seat. Then, fuelsubjected to high pressure is injected through the injection port 7 intothe combustion chamber of the engine until such time as the controlvalve member 22 closes again. The consequence is then that the pressurein the control chamber 15 rises, and because of the prestressing forceof the nozzle spring 12, the nozzle needle 5 is pressed with its tip 6back against the associated nozzle needle seat.

The second exemplary embodiment, shown in FIG. 2, is largely equivalentto the first exemplary embodiment shown in FIG. 1. For the sake ofsimplicity, the same reference numerals are used to designate the sameelements. Also in order to avoid repetition, reference is made to theabove description of the first exemplary embodiment. Below, only thedifferences between the two exemplary embodiments will be addressed.

In the second exemplary embodiment shown in FIG. 2, an auxiliary controlchamber 24 is embodied on the end of the bush 16 remote from thecombustion chamber. The auxiliary control chamber 24 communicates withthe nozzle spring chamber 10 via an inlet throttle 25. The auxiliarycontrol chamber 24 also communicates with the control chamber 15, via anauxiliary throttle 26. In the exemplary embodiment shown in FIG. 2, thebush 16 can lift from its seat on the retaining body 3 in the closingmotion of the nozzle needle 5. The lifting of the bush 16 from its seatis assured by the auxiliary throttle 26. When the control valve member22 closes, the auxiliary control chamber 24 first fills with fuelsubjected to high pressure, and only after that does the control chamber15 fill with such fuel.

The control valve member 22 is shown merely by way of example. Withinthe scope of the present invention, force-balanced magnet valves ordouble-switching piezoelectric actuators could be used equally well.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible, within the spirit and scope of the invention, thelatter being defined by the appended claims.

I claim:
 1. In a common rail injector for injecting fuel in a commonrail injection system of an internal combustion engine, which system hasan injector housing (1) with a fuel inlet (11) that is in communicationwith a central high-pressure fuel reservoir outside the injector housing(1) and with a pressure chamber inside the injector housing (1), fromwhich fuel subjected to high pressure is injected as a function of theposition of a control valve (22) that assures that a nozzle needle (5)movable back and forth and received in a longitudinal bore (4) of theinjector axially counter to the prestressing force of a nozzle spring(12) that is received in a nozzle spring chamber (10), lifts a tip (6)of the nozzle needle from a seat when the pressure in the pressurechamber (8) is greater than the pressure in a control chamber (15) thatcommunicates with the fuel inlet via an inlet throttle (19; 25, 26) andwith a relief chamber via a fuel outlet (20), the improvement whereinthe control chamber (15) is formed, in part, by a substantiallycylindrical recess (14) in an end of the nozzle needle (5), remote fromthe tip (6).
 2. The common rail injector of claim 1, wherein an outercircumferential portion of a bush (16) is axially displaceably receivedwith a sealing effect in said substantially cylindrical recess (14), anend face, remote from tip (6), of which bush is pressed by theprestressing force of the nozzle spring (12) against the injectorhousing (1), and an interior of which bush communicates with the fueloutlet (20).
 3. The common rail injector of claim 2, wherein on the end(16) of the bush, remote from the tip (6), a collar (17) is embodied,which forms an abutment for the nozzle spring (12) that is prestressedcounter to the end of the nozzle needle (5) remote from the tip (6). 4.The common rail injector of claim 3, wherein on the face end of the bush(16), remote from the tip (6), which is in contact with the injectorhousing (1), a biting edge (18) is embodied.
 5. The common rail injectorof claim 4, wherein the fuel inlet (11) communicates with the pressurechamber (8) via the nozzle spring chamber (10), and that the nozzleneedle (5) is guided between the nozzle spring chamber (10) and thepressure chamber (8).
 6. The common rail injector of claim 5, wherein atleast one flat face (9), past which fuel can flow from the nozzle springchamber (10) into the pressure chamber (8), is embodied on the nozzleneedle (5) between the nozzle spring chamber (10) and the pressurechamber (8).
 7. The common rail injector of claim 3, wherein the fuelinlet (11) communicates with the pressure chamber (8) via the nozzlespring chamber (10), and that the nozzle needle (5) is guided betweenthe nozzle spring chamber (10) and the pressure chamber (8).
 8. Thecommon rail injector of claim 7, wherein at least one flat face (9),past which fuel can flow from the nozzle spring chamber (10) into thepressure chamber (8), is embodied on the nozzle needle (5) between thenozzle spring chamber (10) and the pressure chamber (8).
 9. The commonrail injector of claim 3, wherein the inlet throttle (19; 25) isintegrated with the nozzle needle (5) or with the bush (16).
 10. Thecommon rail injector of claim 3, wherein the nozzle needle stroke (H) isdefined by the axial spacing between the nozzle needle (5) and the bush(16).
 11. The common rail injector of claim 2, wherein on the face endof the bush (16), remote from the tip (6), which is in contact with theinjector housing (1), a biting edge (18) is embodied.
 12. The commonrail injector of claim 11, wherein the fuel inlet (11) communicates withthe pressure chamber (8) via the nozzle spring chamber (10), and thatthe nozzle needle (5) is guided between the nozzle spring chamber (10)and the pressure chamber (8).
 13. The common rail injector of claim 12,wherein at least one flat face (9), past which fuel can flow from thenozzle spring chamber (10) into the pressure chamber (8), is embodied onthe nozzle needle (5) between the nozzle spring chamber (10) and thepressure chamber (8).
 14. The common rail injector of claim 2, whereinthe inlet throttle (19; 25) is integrated with the nozzle needle (5) orwith the bush (16).
 15. The common rail injector of claim 2, wherein thenozzle needle stroke (H) is defined by the axial spacing between thenozzle needle (5) and the bush (16).
 16. The common rail injector ofclaim 2, wherein on the end of the bush (16), remote from the tip (6),an auxiliary control chamber (24) is embodied, which communicates via aninlet throttle (25) with the nozzle spring chamber (10) and via anauxiliary throttle (26) with the cylindrical recess (14) in the nozzleneedle (5).
 17. The common rail injector of claim 2, wherein the fuelinlet (11) communicates with the pressure chamber (8) via the nozzlespring chamber (10), and that the nozzle needle (5) is guided betweenthe nozzle spring chamber (10) and the pressure chamber (8).
 18. Thecommon rail injector of claim 17, wherein at least one flat face (9),past which fuel can flow from the nozzle spring chamber (10) into thepressure chamber (8), is embodied on the nozzle needle (5) between thenozzle spring chamber (10) and the pressure chamber (8).
 19. The commonrail injector of claim 1, wherein the fuel inlet (11) communicates withthe pressure chamber (8) via the nozzle spring chamber (10), and thatthe nozzle needle (5) is guided between the nozzle spring chamber (10)and the pressure chamber (8).
 20. The common rail injector of claim 19,wherein at least one flat face (9), past which fuel can flow from thenozzle spring chamber (10) into the pressure chamber (8), is embodied onthe nozzle needle (5) between the nozzle spring chamber (10) and thepressure chamber (8).